Dynamic cell range expansion

ABSTRACT

Methods and systems are provided for calculating a bias value based on radio frequency signal power measurements. A wireless communication device (WCD) measures the powers of radio frequency signals received by the WCD, including a first radio frequency signal transmitted by a first base station of a wireless network and a second radio frequency signal transmitted by a second base station of the wireless network. The first base station transmits radio frequency signals at a higher power than the second base station. The WCD calculates a bias value based on at least one of the measured powers of the first radio frequency signal and the second radio frequency signal. The bias value, in combination with the measured powers of the first and second radio frequency signals, can be used to select one of the first and second base stations.

BACKGROUND

Many people use wireless communication devices (WCDs), such as cellphones and personal digital assistants (PDAs), to communicate withcellular wireless networks. These WCDs typically communicate over aradio frequency (RF) air interface with a wireless network. Wirelessnetworks typically include a plurality of base stations, each of whichprovide one or more wireless coverage areas, such as cells and sectors.When a WCD is positioned in one of these wireless coverage areas, it cancommunicate over the air interface with the base station, and in turnover one or more circuit-switched networks, packet-switched networks,and/or other transport networks to which the base station providesaccess.

Some base stations in cellular wireless networks may be located inpublicly-accessible areas and may be usable by a service provider'scustomers generally. Such base stations are often referred to asproviding wireless coverage in “macrocells.”

Other base stations in cellular wireless networks may transmit at lowerpower levels so to provide wireless coverage in smaller areas, such as“picocells” or “femtocells.” Such base stations may be located inprivate locations, such as residential or business locations, and/or maybe usable by only particular customers. As one example, serviceproviders have recently begun offering consumers devices referred toherein as Low-Cost Internet Base Stations (LCIBs), which may providefemtocell wireless coverage and use a customer's Internet connection asbackhaul.

The wireless coverage provided by a low-power base station with afemtocell or picocell coverage area (e.g., an LCIB) may overlap or beencompassed within a macrocell. In such cases, it may be possible for aWCD to receive wireless service from either the macrocell base stationor from the low-power base station.

OVERVIEW

Methods and systems are provided for calculating bias values based onradio frequency signal power measurements. In some embodiments, awireless communication device (WCD) measures the powers of radiofrequency signals received by the WCD, including a first radio frequencysignal transmitted by a first base station of a wireless network and asecond radio frequency signal transmitted by a second base station ofthe wireless network. The first base station transmits radio frequencysignals at a higher power than the second base station. The WCDcalculates a bias value based on at least one of the measured powers ofthe first radio frequency signal and the second radio frequency signal.The WCD selects a base station from among the first base station and thesecond base station based on at least the measured power of the firstradio frequency signal received from the first base station, themeasured power of the radio frequency signal received from the secondbase station, and the bias value. The WCD transmits one or more messagesto the selected base station requesting a connection to the wirelessnetwork through the selected base station.

In some embodiments, a WCD measures the powers of radio frequencysignals received by the WCD, including a first radio frequency signaltransmitted by a first base station of a wireless network and a secondradio frequency signal transmitted by a second base station of thewireless network. The first base station transmits radio frequencysignals at a higher power than the second base station. The WCDcalculates a bias value based on at least one of the measured powers ofthe first radio frequency signal and the second radio frequency signal.The WCD generates a first report indicative of the measured power of oneof the first and second radio frequency signals and a second reportindicative of the measured power of the other of the first and secondradio frequency signals offset by the bias value. The WCD transmits thefirst and second reports to the wireless network.

In some embodiments, a WCD includes a radio frequency transceiver, aprocessor, and data storage that stores program instructions. Theprogram instructions are executable by the processor to cause the WCD toperform functions. The functions include: (i) measuring powers of radiofrequency signals received by the radio frequency transceiver, includingat least a first radio frequency signal transmitted by a first basestation of a wireless network and a second radio frequency transmittedby a second base station of the wireless network, wherein the first basestation transmits radio frequency signals at a higher power than thesecond base station and (ii) calculating a bias value based on at leastone of the measured powers of the first radio frequency signal andsecond radio frequency signal.

These as well as other aspects and advantages will become apparent tothose of ordinary skill in the art by reading the following detaileddescription, with reference where appropriate to the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a simplified diagram of elements of a wireless network andcells associated with the wireless network, in accordance with anexample embodiment.

FIG. 1B is a simplified diagram of elements of a wireless network andcells associated with the wireless network, in accordance with anexample embodiment.

FIG. 2A is an illustration of monotonically decreasing functions whichtake as an input a measured power of a radio frequency signal and outputa bias value, in accordance with an example embodiment.

FIG. 2B is an illustration of monotonically increasing functions whichtake as an input a calculated signal quality of a radio frequency signaland output a bias value, in accordance with an example embodiment.

FIG. 3 is a simplified block diagram of a wireless communication device,in accordance with an example embodiment.

FIG. 4 is a flowchart of a method, in accordance with an exampleembodiment.

FIG. 5 is a flowchart of a method, in accordance with an exampleembodiment.

DETAILED DESCRIPTION 1. Introduction

A wireless network can include a plurality of base stations that allowwireless communication devices (WCDs) to communicate with the wirelessnetwork. In some examples, a WCD is served by an individual base stationat a time, and can be handed off between base stations. It can bedesirable for a WCD that is being served by a first base station to behanded off to a second base station to avoid disruption of wirelesscommunications between the WCD and the wireless network. For example,the WCD can be a cellphone that is being served by a base station andthat is traveling in a moving vehicle. As the cellphone moves in thevehicle, its distance from the first base station increases, and itsdistance from a second base station decreases. The ability of the WCDand the base stations to wirelessly communicate generally decreases withincreasing distance, so it can be desirable to handoff the WCD from thefirst base station to the second at some point in time to maintain theconnection between the WCD and the wireless network. The determinationthat the WCD could be handed off from one base station to another can bemade based on at least the measured power of radio frequency signalstransmitted by the base stations and received by the WCD. In an example,a WCD being served by a first base station measures the power of radiofrequency signals from the first base station and a second base station.If the measured power of the signal from the second base station isgreater than the measured power of the signal from the first basestation, the WCD may be handed off to the second base station, so thatthe second base station begins serving the WCD.

Other factors could influence the determination that a WCD could behanded off. In an example, the first base station could provide wirelesscoverage in a macrocell, and the second base station could be alower-power base station, such as a low-cost internet base station(LCIB), that provides coverage in a femtocell or picocell. The WCD maymeasure the powers of radio frequency signals from both the first andsecond base stations. The first base station could be serving the WCD,as well as many other devices. Because of the load on the first basestation, it may be desirable to handoff the WCD to the second basestation, even if the measured power of the radio frequency signalreceived from the second base station is less than the measured power ofthe radio frequency signal received from the first base station. Thisconsideration could be implemented by offsetting the measured power ofthe second base station with a bias value. By offsetting the measuredpower of the radio frequency signal received from the second basestation by a bias value, the WCD might be handed off to the second basestation even if the measured power of the radio frequency signals fromthe second base station was less than the measured power of the radiofrequency signals from the first base station, provided that themeasured power corresponding to the second base station was less thanthe measured power corresponding to the first base station by an amountless than the amount of the bias value.

The use of a bias value to affect a determination that a WCD could behanded off from one base station to another base station could result ina WCD handoff which causes an increase in interference in the wirelesscommunications between the WCD and the wireless network. For example, aWCD could be served by a first base station and be able to measure powerlevels of radio frequency signals from the first base station and asecond base station. A bias value could be applied to the measured powercorresponding to the second base station, resulting in a handoff of theWCD from the first base station to the second base station. However, thefirst base station may be transmitting high-power radio frequencysignals which could interfere with wireless communications between theWCD and the second base station. In another example, a WCD is served bya first base station and is able to measure power levels of radiofrequency signals from the first base station and a second base station,and the measured power level corresponding to the first base station isgreater than the measured power level corresponding to the second basestation even after the application of a bias value. As a result, the WCDcontinues to be served by the first base station. However, the radiofrequency signals received from the second base station could have ahigh quality (e.g., they could be relatively free of interference fromthe radio frequency signals transmitted by the first base station), suchthat wireless communication between the WCD and the second base stationwould be acceptable.

To take interference levels into account, a bias value can be based onone or more measured power levels of radio frequency signals received bya WCD. In an example, when making a determination whether to handoff aWCD from a first base station to a second base station that transmitsradio frequency signals at a lower power than the first base station,the bias value could be based on a measured power level of the radiofrequency signals received by the WCD from the first base station. Thebias value could be calculated as the output of a function whose outputdecreases monotonically with an input measured power level of the radiofrequency signals from the first base station. The input measured powerlevel of the first base station could be a reference signal receivedpower (RSRP) of the received signal from the first base station or someother measure of the power level of the received radio frequency signalfrom the first base station. The monotonically decreasing function couldbe a linear function or a non-linear function; example non-linearfunctions could include exponentials, polynomials, piecewise definedfunctions, lookup tables, rational functions, or any other non-linearfunctions which could map an input measured power level of a basestation to an output bias value such that the output bias valuedecreases monotonically with increasing input measured power levels.

In another example, when making a determination that a WCD should behanded off between a first base station and a second base station thattransmits radio frequency signals at a lower power than the first basestation, the bias value could be based on a signal quality level of theradio frequency signals received by the WCD from the second basestation. The bias value could be calculated as the output of a functionwhose output increases monotonically with an input signal quality levelof the radio frequency signals from the second base station. The inputsignal quality level of the first base station could be a referencesignal received quality (RSRQ) calculated based on the received signalfrom the second base station and a received signal strength indicator(RSSI) that accounts for received signals from any other sources whichcould interfere with the received signal from the second base station.The monotonically increasing function could be a linear function or anon-linear function; example non-linear functions could includeexponentials, polynomials, piecewise defined functions, lookup tables,rational functions, or any other non-linear functions which could map aninput calculated quality level of a base station to an output bias valuesuch that the output bias value increases monotonically with increasinginput quality levels. The bias value may be based on the output ofmultiple functions; for example, it could be a weighted sum of theoutput of a monotonically decreasing function of an input measured powerlevel of radio frequency signals received from a first base station andthe output of a monotonically increasing function of an input calculatedquality of radio frequency signals received from a second base station.The weighted sum could also include other factors; for example, it couldinclude a constant offset term that could be based on the load of one ormore of the base stations transmitting radio frequency signals receivedby the WCD.

It is evident to one skilled in the art that the need to handoff a WCDbetween a first base station and a second base station could arise in avariety of scenarios in addition to the examples related above. The WCDcould take the form of a cellphone, a mobile hotspot, a tablet computer,a laptop computer, a personal computer, a wireless-enabled appliance, orany device that is configured to access a wireless network. The basestations could be macro base stations, micro base stations, pico basestations, femto base stations, low-cost internet base stations, otherbase stations configured to serve a WCD and enable wirelesscommunication between the WCD and the wireless network, or anycombination of the above. Changes in the power, quality, or otherproperties of radio frequency signals transmitted by base stations thatare received by a WCD could occur due to a variety of factors, includingrelative motion of the WCD and the base stations, changes in atmosphericconditions, radio frequency noise sources, or any other factors capableof affecting wireless communication between a WCD and a base station. AWCD may be able to measure powers of received radio frequency signalsfrom more than two base stations. The WCD may calculate a bias value byusing measured power levels relating to a base station of the more thantwo base stations corresponding to the highest measured power level andmeasured power levels relating to a base station of the more than twobase stations which is a femtocell or LCIB which is configured to beable to serve the WCD. Bias values could be calculated for comparison ofmore than one pair of base stations; for example, a bias values could becalculated for each pairwise combination of base stations in the set ofbase stations whose transmitted radio frequency signals the WCD canreceive.

A WCD may not be served by any base station at all; for example, a WCDmay not be served by a base station immediately after being powered onor after exiting a mode in which communication features or components ofthe WCD are disabled. In such example scenarios, the methods describedherein could be used to select a base station to serve the WCD, wherethe selected base station is one of a set of base stations which couldserve the WCD. For example, a WCD could be activated and could detectradio frequency signals from a first base station and a second basestation, where the first base station transmits radio frequency signalsat a higher power than the second base station. The decision to servethe WCD with the first or the second base station could be made based ona measured power of the radio frequency signal from the first basestation that is received by the WCD, a measured power of the radiofrequency signal from the second base station that is received by theWCD, and a bias value based on the measured powers of the radiofrequency signals from the first and the second base stations that arereceived by the WCD. The decision could be made by the WCD and the WCDcould transmit a message to the wireless network to request that the WCDbe served by the selected base station. Alternatively, the WCD couldsend messages containing one or more of the measured power of the radiofrequency signal from the first base station that is received by theWCD, the measured power of the radio frequency signal from the secondbase station that is received by the WCD, and the bias value based onthe measured powers of the radio frequency signals from the first andthe second base stations that are received by the WCD to the wirelessnetwork. The wireless network could then use the contents of themessages sent by the WCD to select a base station to serve the WCD.

2. Example Wireless Network

As shown in FIG. 1A, an example wireless network 100 may include a macrobase station 110, a femtocell low-cost internet base station (LCIB) 120,and several wireless communication devices (WCDs) 132, 134, 136.Additional entities could be present, such as additional WCDs,additional macro base stations, additional LCIBs, micro base stations,pico base stations, etc. The illustrated example elements are part of awireless network which facilitates communication between WCDs, betweenWCDs and other networks (e.g., the internet, a public switched telephonenetwork (PSTN), etc.). Example wireless coverage area 112 (whichincludes areas 122 and 124) is an example of an area in which a WCDcould be served by the macro base station 110. WCDs 132, 134, 136 areable to be served by either the macro base station 110 or the LCIB 120.The WCDs 132, 134, 136 are configured to measure powers of radiofrequency signals they receive from base stations (e.g., macro basestation 110 and LCIB 120).

The measured powers can be used to determine whether to handoff a WCD(e.g., 132) from one base station to another. This determination can bemade to avoid disruption of wireless communication between the WCD 132and the wireless network 100. An example determination could be tocompare the measured power of the radio frequency signals from the macrobase station 110 to the measured power of the radio frequency signalsfrom the LCIB 120 and handoff the WCD (e.g., 134) to whichever of themacro base station 110 and LCIB 120 corresponds to the greater measuredpower. Area 122 is an example of an area in which a WCD could measure agreater power corresponding to LCIB 120 and could be served by LCIB 120.

In some embodiments, it could be advantageous to handoff a WCD (e.g.,134) to LCIB 120 from macro base station 110 to reduce the load on macrobase station 110. To make the determination to handoff the WCD 134, themeasured power of the radio frequency signals from the macro basestation 110 could be compared with the measured power of the radiofrequency signals from the LCIB 120 offset by a constant bias value.Area 124 (surrounding area 122) is an example of an area in which a WCDcould measure a greater power corresponding to macro base station 110but the determination could be made to serve WCD 134 by LCIB 120, wherethe determination is based on the measured power of the radio frequencysignals from the macro base station 110 and the measured power of theradio frequency signals from the LCIB 120 offset by the constant biasvalue.

In some instances, the use of a constant bias value in the determinationto handoff a WCD could lead to disruption of wireless communicationsbetween the WCD and the wireless network. In one example, WCD 132 is inarea 124 and is being served by LCIB 120. However, the radio frequencysignals received by the WCD 132 from macro base station 110 could besufficiently powerful that they interfere with communication between WCD132 and LCIB 120. In another example, WCD 136 is being served by macrobase station 110. The measured power of the radio frequency signalstransmitted by macro base station 110 and received by WCD 136 could begreater than the measured power of the radio frequency signalstransmitted by LCIB 120 and received by WCD 136 offset by a constantbias. However, the quality of the radio signals transmitted by LCIB 120and received by WCD 136 could be such that communication between the WCD136 and wireless network 100 could be acceptable.

FIG. 1B shows an example wireless network 101 that includes a macro basestation 111, a femtocell low-cost internet base station (LCIB) 121, andseveral wireless communication devices (WCD) 133, 135, 137. Additionalentities could be present, such as additional WCDs, additional macrobase stations, additional LCIBs, micro base stations, pico basestations, etc. The illustrated example elements are part of a wirelessnetwork which facilitates communication between WCDs, between WCDs andother networks (e.g., the internet, a public switched telephone network(PSTN), etc.). Example wireless coverage area 113 (which includes areas123 and 127) is an example of an area in which a WCD could be served bythe macro base station 111. WCDs 133, 135, 137 are able to be served byeither the macro base station 111 or the LCIB 121. The WCDs 133, 135,137 are configured to measure powers of radio frequency signals theyreceive from base stations (e.g., macro base station 111, LCIB 121).

In some embodiments, it could be advantageous to make the determinationto handoff a WCD (e.g., 135) to avoid disruption of wirelesscommunication between the WCD 135 and the wireless network 101. Anexample determination could be to compare the measured power of theradio frequency signals from the macro base station 111 to the measuredpower of the radio frequency signals from the LCIB 121 and handoff theWCD (e.g., 135) to whichever of the macro base station 111 and LCIB 121corresponds to the greater measured power. Area 123 is an example of anarea in which a WCD could measure a greater power corresponding to LCIB121 and could be served by LCIB 121.

In some embodiments, it could be advantageous to handoff a WCD (e.g.,135) to LCIB 121 from macro base station 111 to reduce the load on macrobase station 111. To make the determination to handoff the WCD 135, themeasured power of the radio frequency signals from the macro basestation 111 could be compared with the measured power of the radiofrequency signals from the LCIB 121 offset by a bias value that is basedon the measured power of the radio frequency signals from the macro basestation 111, the measured power of the radio frequency signals from theLCIB 121, or some combination of these measured powers. Area 127(surrounding area 123) is an example of an area in which a WCD couldmeasure a greater power corresponding to macro base station 111 but thedetermination could be made to serve WCD 135 by LCIB 121, where thedetermination is based on the measured power of the radio frequencysignals from the macro base station 111 and the measured power of theradio frequency signals from the LCIB 121 offset by a bias value that isbased on the measured power of the radio frequency signals from themacro base station 111 and/or the LCIB 121.

The bias value can be calculated as the output of a function that takesthe measured power of a radio frequency signal received by the WCD as aninput. FIG. 2A and FIG. 2B show example functions to take a measuredpower of a radio frequency signal received by a WCD as an input andcalculate an output that can be used as the bias value or from which thebias value can be calculated.

FIG. 2A shows example monotonically decreasing functions 232, 234 whichtake as input a measured power of a radio frequency signal received by aWCD 220 and generate an output bias value 210. Example monotonicallydecreasing functions 232, 234 include a linear function 232 and anonlinear function 234. Example monotonically decreasing functions 232,234 are intended as illustrative examples of monotonically decreasingfunctions which take as input a measured power of a radio frequencysignal received by a WCD 220 and generate an output bias value 210. Inan example, a measured power of a radio frequency signal received by aWCD 220 is a reference signal received power (RSRP) of a macro basestation like macro base station 111 of FIG. 1B. The use of a bias valuecalculated as the output of a monotonically decreasing function of theRSRP of macro base station 111 could result in an area 127 (surroundingarea 123) in which a WCD could measure a greater received radiofrequency signal power corresponding to macro base station 111 but thedetermination could be made to serve the WCD by LCIB 121.

An example determination could take the form p₂+f(p₁)>p₁, where p₁ is anRSRP of macro base station 111, p₂ is an RSRP of LCIB 121, and f( ) is amonotonically decreasing function. This example determination could bemade for RSRPs of macro base station 111 and LCIB 121 measured by WCDs133, 135, and 137. The determination could be true for WCDs 135 and 137;thus, WCDs 135 and 137 could be handed off to LCIB 121. Thedetermination could be false for WCD 133; thus, WCD 133 could continueto be served by macro base station 111.

FIG. 2B shows example monotonically increasing functions 282, 284 whichtake as input a calculated signal quality of a radio frequency signalreceived by a WCD 270 and generate an output bias value 260. Examplemonotonically increasing functions 282, 284 include a linear function282 and a nonlinear function 284. Example monotonically increasingfunctions 282, 284 are intended as illustrative examples ofmonotonically increasing functions which take as input a calculatedquality of a radio frequency signal received by a WCD 270 and generatean output bias value 260. In an example, a calculated quality of a radiofrequency signal received by a WCD 270 is a reference signal receivedquality (RSRQ) of an LCIB like LCIB 121 in FIG. 1B. The RSRQ of LCIB 121could be calculated by dividing a measured power of a radio frequencysignal transmitted by LCIB 121 and received by a WCD by an RSSI valuemeasured by the WCD. The use of a bias value calculated as the output ofa monotonically increasing function of the RSRQ of LCIB 121 could resultin an area 127 (surrounding area 123) in which a WCD could measure agreater radio frequency signal power corresponding to macro base station111 but the determination could be made to serve the WCD by LCIB 121.

An example determination could take the form p₂+g(s₂)>p₁, where p₁ is anRSRP of macro base station 111, p₂ is an RSRP of LCIB 121, s₂ is an RSRQof LCIB 121, and g( ) is a monotonically increasing function. Thisexample determination could be made for RSRPs and RSRQs of macro basestation 111 and LCIB 121 measured by WCDs 133, 135, and 137. Thedetermination could be true for WCDs 135 and 137; thus, WCDs 135 and 137could be handed off to LCIB 121. The determination could be false forWCD 133; thus, WCD 133 could continue to be served by macro base station111.

The examples in FIGS. 1A and 1B described above are meant for purposesof illustration and are not meant to be limiting. The WCD could take theform of a cellphone, a mobile hotspot, a tablet computer, a laptopcomputer, a personal computer, a wireless-enabled appliance, or anydevice that is configured to access a wireless network. The basestations could be macro base stations, micro base stations, pico basestations, femto base stations, low-cost internet base stations, otherbase stations configured to serve a WCD and enable wirelesscommunication between the WCD and the wireless network, or anycombination of the above. A WCD may be able to measure powers ofreceived radio frequency signals from more than two base stations (i.e.,the illustrated macro base stations 110, 111 and LCIBs 120, 121). TheWCD may calculate a bias value by using measured power levels relatingto a base station of the more than two base stations corresponding tothe highest measured power level and calculated signal quality levelsrelating to a base station of the more than two base stations which is afemtocell or LCIB which is configured to be able to serve the WCD. Biasvalues could be calculated for comparison of more than one pair of basestations; for example, a bias value could be calculated for eachpairwise combination of base stations in the set of base stations whosetransmitted radio frequency signals the WCD can receive. The signalquality may be an RSRQ calculated as described above, or the signalquality could be calculated in another manner to generate a measure ofthe quality of signals transmitted by a base station and received by aWCD; for example, the signal quality could be a packet loss ratio, aratio of transmitted signal power to in-band noise signal power, or someother measure of radio frequency signal quality.

The scale of functions 232, 234, 282, 284 is illustrative and not meantto constrain possible functions used in embodiments of the claimedelements. Further, the shape of functions 232, 234, 282, 284 isillustrative; any sort of function could be employed, including a linearfunction, a non-linear function, an exponential function, a polynomialfunction, a piecewise defined function, a lookup table, a rationalfunction, or any other non-linear function which could take an inputpower level or quality level of a radio frequency signal and output abias value such that the output bias value can be used in thedetermination to handoff a WCD. The bias value used in determiningwhether to handoff a WCD could also be based on the outputs of multiplefunctions. In an example, the bias value used in determining whether tohandoff a WCD could be a weighted sum of the output of a monotonicallydecreasing function of a measured power level of a radio frequencysignal received by a WCD and the output of a monotonically increasingfunction of a calculated quality level of a radio frequency signalreceived by the WCD.

3. Example Wireless Communication Device

FIG. 3 is a simplified block diagram of an example wirelesscommunication device (WCD) that could operate in accordance with any ofthe methods described in this disclosure. As illustrated, WCD 300 mayinclude a processor 310, a wireless communication interface 320, antenna322, and data storage 330, all coupled by a system bus 340.

Processor 310 could be, for example, a general purpose microprocessorand/or a discrete signal processor. Though processor 310 is describedhere as a single processor, those having skill in the art will recognizethat WCD 300 may contain multiple (e.g., parallel) processors. Datastorage 330 may store a set of program instructions 332 that areexecutable by processor 310 to carry out one or more of functionsdescribed herein. Alternatively, some or all of the functions couldinstead be implemented through hardware. In addition, data storage 330may store parameters and application data 334 in connection withcarrying out various functions described herein.

Various functions enabled by program instructions 332 contained in datastorage 330 can include measuring the powers of radio frequency signalsreceived by the WCD 300 and calculating bias values based on one or moreof the measured powers. Calculating a bias value could involvecalculating the output of a monotonically decreasing function whichtakes as an input a measured power level of a radio frequency signalreceived by the WCD 300. The measured power level of a radio frequencysignal received by the WCD 300 could be a reference signal receivedpower (RSRP). The monotonically decreasing function could be a linearfunction, a non-linear function, or any other function which takes asinput a measured power level of a radio frequency signal received by theWCD 300 and outputs a bias value which monotonically decreases withincreasing values of the input measured power level. Calculating biasvalues based on one or more of the measured powers could also includecalculating a quality level of a radio frequency signal received by theWCD 300 and calculating the output of a monotonically increasingfunction which takes as an input the calculated quality level of a radiofrequency signal received by the WCD 300. The calculated quality levelof a radio frequency signal received by the WCD 300 could be a referencesignal received quality (RSRQ). The monotonically increasing functioncould be a linear function, a non-linear function, or any other functionwhich takes as input a calculated quality level of a radio frequencysignal received by the WCD 300 and outputs a bias value whichmonotonically increases with increasing values of the input calculatedquality level. Calculating bias values based on one or more of themeasured powers could also include calculating a weighted sum of aplurality of bias values based on the measured powers that arecalculated as described above.

Various functions enabled by instructions contained in data storage 330can further include instructions enabling the selection of a basestation and/or transmission of radio frequency signals based on themeasured powers of radio frequency signals and the calculated biasvalues. For example, the WCD 300 could select a base station based onthe measured powers of radio frequency signals received by the WCD 300and the bias values calculated by the WCD 300. The WCD 300 could furthertransmit to the selected base station a request to be served by theselected base station. In another example, a WCD could generate a reportbased on the measured powers of radio frequency signals received by theWCD 300 and the bias value calculated by the WCD 300. The WCD 300 couldthen transmit the generated report to the wireless network. Data storage330 can further include instructions enabling other operations of theWCD 300, including operation of a user interface, operating sensorsincluded in the WCD, making connections with the PSTN through thewireless network and allowing a user of the WCD 300 to make a telephonecall, or other functions of the WCD 300 according to an application ofthe WCD 300.

Wireless communication interface 320 may include a chipset suitable forcommunicating with one or more devices over antenna 322. Suitabledevices may include, for example, elements of a wireless network. Theseelements could include macro base stations, micro base stations, picobase stations, femto base stations, low-cost internet base stations(LCIBs), or other suitable devices capable of wireless communication.The chipset could be suitable for communication using Long TermEvolution (LTE) protocols. Alternatively or additionally, the chipset orwireless-communication interface 320 may be able to communicate withother types of networks and devices, such as EV-DO networks, GSMnetworks, UMTS networks, HSPA networks, WiMAX networks, CDMA networks,Wi-Fi networks, Bluetooth devices, and/or one or more additional typesof networks and devices.

WCD 300 can be a stand-alone device, like a cellular telephone, tabletcomputer, laptop computer, personal computer, or mobile hotspot. If theWCD 300 is a stand-alone device, it can include batteries, rechargingcircuitry, user interface components, GPS receivers, Bluetoothinterfaces, WiFi interfaces, infrared transceivers, displays,accelerometers, and/or other components enabling additional functions ofthe stand-alone device. Data storage 330 can additionally includeprogram instructions for operating the aforementioned additionalcomponents and for enabling the stand-alone function of the WCD 300.

WCD 300 can also be implemented as a component, subassembly, orsubsection of another device. For example, WCD 300 could be configuredas a MiniPCI card designed to be installed into a portable computer. WCD300 could also be configured as a PCI card, a PCI-express card, aMiniPCI-express card, a PCMCIA card, a PC card, or to use otherinterfaces or to comply with other physical formats. WCD 300 could alsobe implemented to connect via a USB, firewire, ATA, serial, parallel, orother wired or wireless communication method. WCD 300 could be a singleintegrated circuit chip or several chips and other components assembledonto a printed circuit board or by other means to form a component orsub-assembly. The component or sub-assembly could be configured to beassembled into a device with other components. Said device could beconfigured to be operated on its own or as a component or sub-assemblyof a more extensive device.

4. Example Methods

FIG. 4 is a flowchart of an example method 400 carried out by a wirelesscommunication device (WCD), such as the WCD depicted in FIG. 3. As shownin FIG. 4, the method 400 begins at step 402, in which the WCD measurespowers of radio frequency signals received by the WCD. The radiofrequency signals received by the WCD include at least a first radiofrequency signal transmitted by a first base station of a wirelessnetwork and a second radio frequency transmitted by a second basestation of the wireless network, wherein the first base stationtransmits radio frequency signals at a higher power than the second basestation.

The first and second base stations of the wireless network can be macrobase stations, micro base stations, pico base stations, femto basestations, low-cost internet base stations (LCIBs), or any other basestation configured to serve the WCD and facilitate communication betweenthe WCD and the wireless network, or any combination of above types ofbase station. While the first base station transmits radio frequencysignals at a higher power than the second base station, the power levelof the radio frequency signals transmitted by the first base station andreceived by the WCD is not necessarily greater than the power level ofthe radio frequency signals transmitted by the second base station andreceived by the WCD. Radio frequency signals transmitted by the firstand second base stations can be attenuated by a variety of factors,including distance between the base station and the WCD, line-of-sightbetween the base station and the WCD, buildings or geography in theenvironment of the base station and the WCD, or any other factor capableof affecting radio frequency signals. The measured powers of radiofrequency signals can include measured powers of radio frequency signalstransmitted by base stations other than the first and second basestations. In examples where the measured powers of radio frequencysignals include measured powers of radio frequency signals transmittedby more than two base stations, the second base station could be an LCIBand the first base station could be a base station of the remaining morethan one base station corresponding to the radio frequency signalreceived by the WCD from the remaining more than one base station withthe greatest measured power.

Method 400 also includes step 404, in which the WCD calculates a biasvalue based on at least one of the measured powers of the first radiofrequency signal and second radio frequency signal. In an example, thebias value could be calculated as the output of a monotonicallydecreasing function of the measured power level of the first radiofrequency signal. The measured power level could be a reference signalreceived power (RSRP) of the first radio frequency signal. Themonotonically decreasing function could be a linear function, anexponential function, a polynomial function, a piecewise definedfunction, a lookup table, a rational function, or any other functionwhich could take an input measured power level of a radio frequencysignal and output a bias value such that the output bias value decreaseswith increasing levels of the input measured power level. The input tothe function could be some measure of the power level of the first radiofrequency signal than the RSRP. In another example, the bias value couldbe calculated as the output of a monotonically increasing function of acalculated signal quality level of the second radio frequency signal.The calculated quality level could be a reference signal receivedquality (RSRQ) of the second radio frequency signal. The RSRQ could becalculated by dividing the measured power level of the second radiofrequency signal by an RSSI value measured by the WCD. The monotonicallyincreasing function could be a linear function, an exponential function,a polynomial function, a piecewise defined function, a lookup table, arational function, or any other function which could take an inputquality level of a radio frequency signal and output a bias value suchthat the output bias value increases with increasing levels of the inputquality level. The input to the function could be some other measure ofthe quality level of the second radio frequency signal than the RSRQ.The calculated quality level could be a packet loss ratio, a ratio oftransmitted signal power to in-band noise signal power, or some othermeasure of radio frequency signal quality. The calculated bias valuecould be a weighted sum of other calculated bias values, for example aweighted sum of the two example bias values described above. Thecalculated weighted sum could also include a constant offset related tothe load of one or both of the first and second base stations.

Method 400 further includes step 406, the WCD selecting a base stationfrom among the first base station and the second base station based onat least the measured power of the first radio frequency signal receivedfrom the first base station, the measured power of the radio frequencysignal received from the second base station, and the bias value. In anexample, the base station corresponding to the greater of the measuredpower level of the first radio frequency signal and the measured powerlevel of the second radio frequency signal offset by the calculated biasvalue is selected. Selection could also include other factors, includingwhether one of the first and second base stations provides a desiredservice to the WCD, whether being served by one of the first and secondbase stations will incur an additional fee, or other factors.

Method 400 additionally includes step 408, the WCD transmitting one ormore messages to the selected base station, wherein the one or moremessages request a connection to the wireless network through theselected base station. Messages could include identification informationcorresponding to the WCD, a listing of services requested by the WCD,the power levels measured by the WCD, the power levels measured by theWCD offset by the bias value calculated by the WCD, or other informationrelated to requesting that the base station facilitate a connectionbetween the WCD and the wireless network. The connection requested bythe WCD could be an initial connection to the wireless network in thecase that the WCD is not already being served by the wireless network.Alternatively, the connection request could be a request to handoff anexisting session with the wireless network to the selected base station.

FIG. 5 is a flowchart of an example method 500 carried out by a wirelesscommunication device (WCD), such as the WCD depicted in FIG. 3. As shownin FIG. 5, the method 500 begins at step 502, in which the WCD measurespowers of radio frequency signals received by the WCD. The radiofrequency signals received by the WCD include at least a first radiofrequency signal transmitted by a first base station of a wirelessnetwork and a second radio frequency transmitted by a second basestation of the wireless network, wherein the first base stationtransmits radio frequency signals at a higher power than the second basestation. The first and second base stations of the wireless network canbe macro base stations, micro base stations, pico base stations, femtobase stations, low-cost internet base stations (LCIBs), or any otherbase station configured to serve the WCD and facilitate communicationbetween the WCD and the wireless network, or any combination of abovetypes of base station. While the first base station transmits radiofrequency signals at a higher power than the second base station, thepower level of the radio frequency signals transmitted by the first basestation and received by the WCD is not necessarily greater than thepower level of the radio frequency signals transmitted by the secondbase station and received by the WCD. Radio frequency signalstransmitted by the first and second base stations can be attenuated by avariety of factors, including distance between the base station and theWCD, line-of-sight between the base station and the WCD, buildings orgeography in the environment of the base station and the WCD, or anyother factor capable of affecting radio frequency signals. The measuredpowers of radio frequency signals can include measured powers of radiofrequency signals transmitted by base stations other than the first andsecond base stations; in examples where the measured powers of radiofrequency signals include measured powers of radio frequency signalstransmitted by more than two base stations, the second base stationcould be an LCIB and the first base station could be a base station ofthe remaining more than one base station corresponding to the radiofrequency signal received by the WCD from the remaining more than onebase station with the greatest measured power.

Method 500 also includes step 504, in which the WCD calculates a biasvalue based on at least one of the measured powers of the first radiofrequency signal and second radio frequency signal. In an example, thebias value could be calculated as the output of a monotonicallydecreasing function of the measured power level of the first radiofrequency signal. The measured power level could be a reference signalreceived power (RSRP) of the first radio frequency signal. Themonotonically decreasing function could be a linear function, anexponential function, a polynomial function, a piecewise definedfunction, a lookup table, a rational function, or any other functionwhich could take an input measured power level of a radio frequencysignal and output a bias value such that the output bias value decreaseswith increasing levels of the input measured power level. The input tothe function could be some measure of the power level of the first radiofrequency signal than the RSRP. In another example, the bias value couldbe calculated as the output of a monotonically increasing function of acalculated quality level of the second radio frequency signal. Thecalculated quality level could be a reference signal received quality(RSRQ) of the second radio frequency signal. The RSRQ could becalculated by dividing the measured power level of the second radiofrequency signal by the measured power level of noise radio frequencysignals in the same frequency band as the second radio frequency signal.The monotonically increasing function could be a linear function, anexponential function, a polynomial function, a piecewise definedfunction, a lookup table, a rational function, or any other functionwhich could take an input quality level of a radio frequency signal andoutput a bias value such that the output bias value increases withincreasing levels of the input quality level. The input to the functioncould be some other measure of the quality level of the second radiofrequency signal than the RSRQ. The calculated quality level could be apacket loss ratio, a ratio of transmitted signal power to in-band noisesignal power, or some other measure of radio frequency signal quality.The calculated bias value could be a weighted sum of other calculatedbias values, for example a weighted sum of the two example bias valuesdescribed above. The calculated weighted sum could also include aconstant offset related to the load of one or both of the first andsecond base stations.

Method 500 additionally includes step 506, the WCD generating a firstreport indicative of the measured power of one of the first and secondradio frequency signals; and step 508, the WCD generating a secondreport indicative of the measured power of the other of the first andsecond radio frequency signals offset by the bias value. As an exampleof steps 506 and 508, the first report could include an RSRP of thefirst radio frequency signal and the second report could include an RSRPof the second radio frequency signal offset by the calculated bias. Inanother example, the first report could include an RSRP of the secondradio frequency signal and the second report could include an RSRP ofthe first radio frequency signal offset by the calculated bias. Othermeasures of the power of the first and second radio frequency signalscan be included in the generated reports instead of or in addition tothe RSRP of the first and second radio frequency signals.

Method 500 further includes step 508, the WCD transmitting the first andsecond reports to the wireless network. The first and second reportscould be included in the same transmission, or the first and secondreports could be included in separate transmissions. The first andsecond reports could be transmitted by the WCD as part of a regularstatus transmission or could be transmitted based on a triggercondition, such as a determination that the WCD might be better servedby one of the first and second based stations by which the WCD was notcurrently being served. The transmission could include information notrelated to the first and second reports, for example identificationinformation corresponding to the WCD, a listing of services requested bythe WCD, or other information related to the operation of the WCD and/orsignals received by the WCD.

The wireless network may receive the first and second reports anddetermine based on these reports whether the WCD should be served by thefirst base station or the second base station. In an example, thewireless network makes this determination based on a comparison of themeasured power indicated by the first report to the measured powerindicated by the second report (which is offset by the bias value). Ifthe first report indicates the greater measured power, the wirelessnetwork may select the base station corresponding to the first reportand instruct the WCD to use that selected base station. If the secondreport indicates the greater measured power (for example, because of theoffset value), the wireless network may select the base stationcorresponding to the second report and instruct the WCD to use thatselected base station. The wireless network's selection could alsoinclude other factors, such as the respective loads of the first andsecond base stations, the respective services available through thefirst and second base stations, and/or other factors

5. Conclusion

Various example embodiments have been described above. Those skilled inthe art will understand, however, that changes and modifications may bemade to those examples without departing from the scope of the claims.

What is claimed is:
 1. A method, comprising: a wireless communicationdevice (WCD) measuring powers of radio frequency signals received by theWCD, wherein the radio frequency signals received by the WCD include atleast a first radio frequency signal transmitted by a first base stationof a wireless network and a second radio frequency signal transmitted bya second base station of the wireless network, wherein the first basestation transmits radio frequency signals at a higher power than thesecond base station; the WCD calculating a bias value based on at leastone of the measured powers of the first radio frequency signal andsecond radio frequency signal; the WCD generating a first reportindicative of the measured power of one of the first and second radiofrequency signals; the WCD generating a second report indicative of themeasured power of the other of the first and second radio frequencysignals offset by the bias value; and the WCD transmitting the first andsecond reports to the wireless network.
 2. The method of claim 1,wherein the first base station provides wireless coverage in a macrocelland the second base station provides wireless coverage in a femtocell orpicocell.
 3. The method of claim 1, wherein the radio frequency signalsreceived by the WCD further include one or more additional radiofrequency signals transmitted by one or more additional base stations ofthe wireless network, and wherein the measured power of the first radiofrequency signal is greater than the measured powers of the one or moreadditional radio frequency signals.
 4. The method of claim 1, whereinthe wireless network is configured to select a serving base station forthe WCD from among the first and second base stations based on the firstand second reports.
 5. The method of claim 1, wherein calculating a biasvalue based on at least one of the measured powers of the first radiofrequency signal and second radio frequency signal comprises (i) usingthe measured power of the first radio frequency signal as an input valueto a function to obtain an output value and (ii) calculating the biasvalue based at least on the output value, wherein the function providesoutput values that decrease monotonically with increasing input values.6. The method of claim 5, wherein the measured power of the first radiofrequency signal is a Reference Signal Received Power (RSRP) of thefirst radio frequency signal.
 7. The method of claim 1, whereincalculating a bias value based on at least one of the measured powers ofthe first radio frequency signal and second radio frequency signalcomprises (i) calculating a signal quality of the second radio frequencysignal based on the measured power of the second radio frequency signal,(ii) using the calculated signal quality of the second radio frequencysignal as an input value to a function to obtain an output value, and(iii) calculating the bias value based at least on the output value,wherein the function provides output values that increase monotonicallywith increasing input values.
 8. The method of claim 7, wherein thesignal quality of the second radio frequency signal is a ReferenceSignal Received Quality (RSRQ) of the second radio frequency signal. 9.A wireless communication device (WCD), comprising: a radio frequencytransceiver; a processor; data storage; and program instructions storedin the data storage, wherein the program instructions are executable bythe processor to cause the WCD to perform functions, the functionscomprising: measuring powers of radio frequency signals received by theradio frequency transceiver, wherein the radio frequency signalsreceived by the radio frequency transceiver include at least a firstradio frequency signal transmitted by a first base station of a wirelessnetwork and a second radio frequency transmitted by a second basestation of the wireless network, wherein the first base stationtransmits radio frequency signals at a higher power than the second basestation; calculating a bias value based on at least one of the measuredpowers of the first radio frequency signal and second radio frequencysignal; generating a first report indicative of the measured power ofone of the first and second radio frequency signals; generating a secondreport indicative of the measured power of the other of the first andsecond radio frequency signals offset by the bias value; andtransmitting the first and second reports to the wireless network. 10.The wireless communication device of claim 9, wherein the functionsfurther comprise: selecting a base station from among the first basestation and the second base station based on at least the measured powerof the first radio frequency signal received from the first basestation, the measured power of the radio frequency signal received fromthe second base station, and the bias value; and transmitting one ormore messages to the selected base station, wherein the one or moremessages request a connection to the wireless network through theselected base station.
 11. The wireless communication device of claim 9,wherein calculating a bias value based on at least one of the measuredpowers of the first radio frequency signal and second radio frequencysignal comprises (i) using the measured power of the first radiofrequency signal as an input value to a function to obtain an outputvalue, wherein the measured power of the first radio frequency signal isa Reference Signal Received Power (RSRP) of the first radio frequencysignal; and (ii) calculating the bias value based at least on the outputvalue, wherein the function provides output values that decreasemonotonically with increasing input values.
 12. The wirelesscommunication device of claim 9, wherein calculating a bias value basedon at least one of the measured powers of the first radio frequencysignal and second radio frequency signal comprises (i) calculating asignal quality of the second radio frequency signal based on themeasured power of the second radio frequency signal; (ii) using thecalculated signal quality of the second radio frequency signal as aninput value to a function to obtain an output value, wherein the signalquality of the second radio frequency signal is a Reference SignalReceived Quality (RSRQ) of the second radio frequency signal; and (iii)calculating the bias value based at least on the output value, whereinthe function provides output values that increase monotonically withincreasing input values.